My T has a PhD, I never use her name in session (what's the point, it's just the two of us, who else would I be talking to?) but in my head I think of her by her first name. When I make appointments on the phone with the front desk I always say "I need an appointment with [First name Last name]," sometimes the person at the desk will also refer to her by her first/last name, sometimes they call her Dr. [Last name], it depends on which person is at the desk